View Full Version : Life in a close cluster & likelihood of them having interstellar travel

2012-Dec-17, 02:02 PM
This thread (http://cosmoquest.org/forum/showthread.php/52283-are-there-many-stars-between-the-galaxies) got me thinking (probably not originally...) about the inverse case: a hypothetical, technological civilization in a close cluster, like a globular cluster.

Assume that there are stable stellar systems with habitable planets, and that one or more of them has developed technology roughly equivalent to current human technology. Further, assume that the society has comparable social mores and economic bases as our human culture.

What is the likelihood of a serious attempt at interstellar probes being launched in the next few decades?

Do note that this conversation is not intended to be about the Earth in its current position, but the "Earth" if it were moved, with "us" to a comparable position in a close cluster, where the nearest star was a light year or less distant.

2012-Dec-17, 02:20 PM
Probably a lot better. Radio transmissions at least would have been detected, and maybe even communication established before actual visual confirmation.

But, to be devil's advocate, would several solar systems in a cluster this close be stable?

2012-Dec-17, 02:55 PM
It is thought that many proto planets escaped our solar system before and during bombardment, by doing sling shot maneuvers, so bombardment likely continues in large dense clusters, except those that are almost 13 billion years old, as a dense cluster has a much larger and deeper gravity well than our Oort cloud = escape from the cluster is rare. Possibly there are a thousand planets for every planet bound to a star, and those bound are mostly tide locked and 1000 k hotter facing their star compared to facing away from their star = not a good place to evolve life on the surface, as the cool terminator gets sterilzed by a close passing star perhaps several times per million years. Life can however evolve under the ice cap of the usually dark side, but technialogically advanced life seems unlikely to evolve anywhere, but perhaps it does at one or two locations that are atypical. Travel to another star may possibly be, not much more difficult on rare occasions than it is for us to go to Mars. They have extra incentive when they calculate that half their planet will likely be sterilized by a star that will barely miss in 71 years or there abouts. Neil

2012-Dec-17, 11:31 PM
Gas Giants in Hot Water: Inhibiting Giant Planet Formation and Planet Habitability in Dense Star Clusters Through Cosmic Time (http://arxiv.org/abs/1212.2662)

2012-Dec-21, 10:33 PM
Well crap. I guess the best you can hope for is for an inhabited system to move near a cluster

2012-Dec-21, 11:00 PM
Note that the paper only concludes that some clusters were dense enough to prevent individual star systems within the core to have an ice line. I don't really see how this is supposed to be a problem for habitability, though.

According to some theories, a gas giant may be necessary for habitability. Why? One theory is that they help protect a planet from excessively frequent extinction event impactors. But these clusters seems to do that already by preventing so many impactors from forming in the first place.

Another theory is that they help fling away comets into an Oort cloud, providing a source for water and other volatiles to deposit themselves into habitable zone planets via impacts. But it seems to me that even if an individual star system deep in the core lacks an ice line, the cluster as a whole still as an ice line. There's got to be some radius beyond which comets will happily survive. They might not be bound to an individual star system, but that just means they'll be meandering around the cluster in a shared Oort cloud instead.

It just seems to me, intuitively, that the role a gas giant may play in traditional single system theories could be played by stronger tugs of nearby stars instead. At the very least, more detailed analysis is required.

A more worrysome factor, I think, could be simply that there is no traditional habitable zone in the densest part of a dense cluster. The only planets with stable orbits may be too close to their host stars to be considered in the traditional habitable zone--think "hot Mercury". On the other hand, such planets might still be habitable anyway, if not in the traditional sense. With 1:1 tide lock, and no thick atmosphere, the dark side could be covered in thick ice, with a subsurface ocean. All those comets meandering through the cluster could deposit this ice, just as comets deposited ice on Mercury (it all melted except for the bits that were lucky enough to end up in appropriate polar craters).

That said, there's nothing wrong with the scenario of an already inhabited isolated system passing through a cluster.

2012-Dec-31, 03:30 PM
Stability requirements aside, I'm not sure living in a cluster would make interstellar travel more likely. Note that since all the bright, important stars would be much closer, they would also be much easier to study from "Earth" than they are for us, reducing the incentive to get up close and personal. On the other hand, stars outside the cluster would seem ridiculously far, perhaps further reducing the impulse to go beyond the cluster. Habitable planets would be no less the decisive factor for them than for us, since even at half a light-year we'd be talking about an enormously difficult achievement with near-term technology.

2012-Dec-31, 04:18 PM
These hypothetical aliens wouldn't need to go out of their way to leave the cluster. Clusters lose stars all the time.

2013-Jan-05, 06:58 PM
Now a rogue planet passing through the densest part of a cluster may have a habitability zone everywhere around it if it gets close enough to the closest starts. A good temporary base maybe?